1. Field of the Invention
The present invention relates to a changeable-lens camera and camera system having an autofocus (AF) detection device of a through-the-lens TTL phase difference system, particularly to a technique of correcting AF in accordance with chromatic aberration of a photographic lens or the like. The present invention relates to a focus detection device, particularly to a focus detection device of a camera, in which the focal point is corrected in accordance with the source of light impinging on a photographic lens in order to reduce the influence of the chromatic aberration of the photographic lens or the like.
2. Description of the Related Art
In a camera on which a through-the-lens (TTL) phase difference autofocus (AF) device is mounted, even when the focus of a photographic lens is adjusted based on focus information detected by the AF device, an image is sometimes out of focus in a case where the image is photographed under illumination by different light sources. This is because a difference occurs between best image plane positions with respect to the respective light sources because of the chromatic aberration characteristic of the photographic lens.
To solve the problem, a technique is described in Jpn. Pat. KOKOKU Publication No. 3-73847 in which a correction amount (hereinafter referred to as AF correction data) of the best image plane position in accordance with the chromatic aberration characteristic is stored in the photographic lens beforehand, and the output of the AF device is corrected based on the AF correction data.
Additionally, in a changeable-lens camera, an intermediate adapter can be attached between the camera and an interchangeable lens to thereby change the focal length. As the intermediate adapter, for example, a teleconverter which increases the focal length or the like has been known.
When the intermediate adapter is attached to the camera, the chromatic aberration due to the intermediate adapter also influences the focal point in the same manner as that of the interchangeable lens. To solve the problem, a technique has been described in Jpn. Pat. No. 3345890 in which the above-described AF correction data is stored beforehand both in the interchangeable lens and the intermediate adapter, and combined to thereby correct the output of the AF device.
Moreover, a technique for detecting luminance of a subject and background light during photography to thereby perform correction at a distance measuring time has heretofore been developed. For example, in Jpn. Pat. Appln. KOKAI Publication No. 9-211306, a so-called phase difference AF system of an automatic focus adjustment device has been described which detects a focal state of a measurement object from the positional relationship between a pair of formed images in a pair of light receiving element rows and which adjusts the focus of the photographic lens in accordance with the detection result.
In general, in a camera or the like adopting this AF system, a subject image is formed by light transmitted through the photographic lens or the like. However, it is well known that a phenomenon is seen in which the focused position of the subject image at this time differs with the wavelength of the light source impinging on the photographic lens or the like.
For example, when photography is performed indoors, the subject is sometimes illuminated using an artificial light source such as a tungsten lamp or a flood lamp. In this case, the focused position of the subject image is sometimes shifted by the influence of an opposite characteristic of the photographic lens or the like, that is, by chromatic aberration or the like. As a countermeasure for the above-described problem, in Jpn. Pat. Appln. KOKAI Publication No. 2003-241064, a focus detection device has been described in which chromatic aberration correction data for a specific wavelength with respect to a reference wavelength is memorized in the interchangeable lens, and correction data is calculated based on the major color of the subject light, measured by colorimetry means for measuring the color of the subject light, to thereby correct the focus.
The device described in this Jpn. Pat. Appln. KOKAI Publication No. 2003-241064 performs complex calculation based on the chromatic aberration correction data for the specific wavelength with respect to the reference wavelength, and the major color of the subject light measured by the colorimetry means for measuring the color of the subject light to thereby calculate a correction value.